1. Field of the Invention
The present invention relates to an apparatus for fixing and recording toner images on various different recording materials. The present invention is particularly advantageous upon recording colored images, and can be applied to all of the types of image forming and recording systems which have currently been utilized, such as copying machines, laser printers, printing machines, facsimiles and others.
2. Description of the Prior Art
The prior art includes Japanese Patent Publication No. 51-10490 in which toner images are fixed to recording materials taking account of the thickness or color thereof, and Japanese Laid-open Patent Application Nos. 51-78342 and 52-20841 in which attention is paid to the color of toner images.
Of these Publications, Japanese Patent Publication No. 51-10490 discloses controlling temperature of fixation so that it is increased as the thickness of recording materials increases. Such a method can follow the different thickness of the recording materials but not the kind of toner images to be fixed on recording materials and the property of the recording materials. In addition, if the temperature of fixation is simply changed, there is produced an "offset" phenomenon in which a toner image is undesirably transferred onto the surface of a contact heating type fixing roller that is recently being utilized wide in the art.
On the contrary, Japanese Laid-open Patent Application Nos. 51-78342 and 52-20841 disclose a technical concept in which paper with an increased thickness is more slowly moved under a radiantly heating lamp of non-contact fixture type when a multicolor toner image is formed thereon in comparison with case where a single-color toner image is formed on paper with a reduced thickness in a color copying machine. However, they are irrelevant to a problem with respect to offset, which will be described hereinafter, since the non-contact type lamp is used therein, and have no teaching as to how to meet the property change and state change of the recording material. In addition, the temperature of fixation is maintained constant in either of the monochromatic or multi-color toner image.
It has also been proposed that the speed of recording paper at which it is being moved between a pair of fixing rollers is changed depending upon the thickness of that recording paper at a constant temperature. However, such a proposal has no variable control to meet variations in recording material and/or colored toner image, and no temperature control.
Under such a state and tendency of art, the present invention is directed to a recording system which can satisfactorily overcome various problems in the prior art, which will be described below.
First of all, the technical background concerning the present invention will first be described. The modern recording systems can utilize plain paper of various different types, such as thick paper, thin paper, postal or post cards and others. It is also strongly demanded to use synthetic resin films which is used in over-head projectors (hereinafter called simply "OHP"). In the prior art, toner images could only temporarily be fixed on the synthetic resin films for some period of time. And, the resulting images were rather easily be damaged and were not the faithfully reproduced images. Namely, the prior art systems does not provide a satisfactory formation of fixed images on the synthetic resin films with respect to fixation and sharpness.
The modern recording systems can provide both multi-color and monochromatic images, the monochromatic images being obtained with different colors respectively. In such a recording system that multicolor and monochromatic modes can selectively be changed from one to another, the fixation of multicolor images is inferior to that of monochromatic images. Therefore, "offset" toner will be increased in amount in the multi-color mode. This adversely affects the fixation of monochromatic image fixation and additionally highly decrease the ability of a rotatable fixing member which contacts the toner images for fixation. Consequently, the rotatable fixation member must frequently be exchanged.
When images are to be recorded on synthetic resin films, the above problem with respect to the rotatable fixation member contacting the toner images cannot be avoided because of the decreased ability of fixation and more offset toner. It is substantially impossible to record colored toner images, particularly on transparent film of synthetic resin, which is more strongly required in the art. There are many newly created problems relating to sharpness, fixation and offset.
One of the newly created problems is that a greater amount of a toner image is transferred to a rotatable member such as a fixing roller, fixing belt or the like, which is used to fix the toner images onto synthetic resin film. In such a case, the rotatable member immediately becomes inoperative. Another problem is that the colored toner images are so unsatisfactorily fixed on the synthetic resin film that the resulting images are rather highly different from the original in color tone.
The problem of color tone associated with the formation of images on synthetic resin films will now be described.
Even if a color image is heatedly fixed on a synthetic resin film as in the prior art fixation of color image, the fixed image will have no practicable color tone when it is projected onto a screen through the OHP. For example, the projected image of yellow-colored toner becomes dark as a whole with the half-tone portion thereof being gray-colored. The projected images of cyan- and magenta-colored toners also become dark as a whole with the color tones being shifted into light green- and red-colors, respectively. This is not practicable.